(DRAFT) - Taxonomy
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
TAXONOMY
NAME - TORTOISE, DESERT
OTHER COMMON NAMES - TORTOISE and DESERT
ELEMENT CODE -
CATEGORY - Reptiles
PHYLUM AND SUBPHYLUM - CHORDATA,
CLASS AND SUBCLASS - REPTILIA,
ORDER AND SUBORDER - TESTUDINES,
FAMILY AND SUBFAMILY - TESTUDINIDAE,
GENUS AND SUBGENUS - XEROBATES,
SPECIES AND SSP - AGASSIZII,
SCIENTIFIC NAME - XEROBATES AGASSIZII
AUTHORITY -
TAXONOMY REFERENCES -
COMMENTS ON TAXONOMY -
Desert Tortoise
Xerobates agassizii (Cooper, 1863)
KINGDOM: Animal GROUP: Reptile
PHYLUM: Chordata CLASS: Reptilia
ORDER: Testudines FAMILY: Testudinidae
The desert tortoise has a high-domed shell, usually with
prominent growth lines on shields of both carapace and plastron.
Carapace is horn-colored or brown, often with yellowish centers in the
laminae. Plastron is yellow shaded with brown along the laminae
edges. Average shell length is 6 to 14 1/2 inches. The head is
relatively small and rounded in front with alveolar ridges of the
upper jaws forming a sharp angle. The hind legs are cylindrical and
columnar. Front legs are covered with large conical scales. Both
legs and neck are retractile with limbs completely closing the shell
opening when drawn in. The male has a longer tail, longer gular
projections at the fore end of the plastron, more thickened nails, and
more concave plastron than the female (01).
The desert tortoise (Xerobates agassizii) was first described by
Cooper in 1863 and was one of four species in the genus Gopherus. It
was considered a monotypic species and the Beaver Dam Slope population
Taxonomy - 1 (DRAFT) - Taxonomy
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
is not currently recognized by some as being taxonomically distinct.
However, due to the restricted movement of tortoises, it is partially
isolated, with a limited amount of gene flow possible between the Utah
and Arizona populations. The genus Xerobates has been resurrected for
this species and is separated from Gopherus by head and skull
morphology (07). The scientific names used for Xerobates agassizii
include Gopherus agassizii, Gopherus agassizi, and Scaptochelys
agassizii.
Taxonomy - 2 (DRAFT) - Status
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
STATUS
Coded Status
T: Federal Threatened
Pest
Commercial
COMMENTS ON STATUS -
U.S. STATUSES AND LAWS:
The Beaver Dam Slope, UT, population of the desert tortoise
(Xerobates agassizii) has been designated a Threatened species
pursuant to the Endangered Species Act of 1973 (50 CFR 17.11;
P.L. 93-205, 87 Stat. 884; 16 U.S.C. 1531-1540), as amended. Critical
Habitat has been designated in Washington County, UT (50 CFR
17.95(c)).
This species is protected by the Lacey Act (P.L. 97-79, as
amended; 16 U.S.C. 3371 et seq.) which makes it unlawful to import,
export, transport, sell, receive, acquire, or purchase any wild
animal (alive or dead including parts, products, eggs, or offspring):
(1) in interstate or foreign commerce if taken, possessed,
transported or sold in violation of any State law or
regulation; or
(2) if taken or possessed in violation of any U.S. law,
treaty, or regulation or in violation of Indian tribal law.
It is also unlawful to possess any wild animal (alive or dead
including parts, products, eggs, and offspring) within the U.S.
territorial or special maritime jurisdiction (as defined in
18 U.S.C. 7) that is taken, possessed, transported, or sold in
violation of any State law or regulation, foreign law, or Indian
tribal law.
RESPONSIBLE FEDERAL AGENCIES:
USFWS -Responsible for the management/recovery, listing, and
law enforcement/protection of this species.
BLM -Responsible for the law enforcement/protection of this
species with applicable State and Federal laws on
public land under their control (43 CFR 4140). Also
responsible for management/recovery on Bureau of Land
Management lands.
All Federal agencies have responsibility to ensure that any
action authorized, funded, or carried out by that agency is not likely
to jeopardize the continued existence of the species or result in the
destruction or adverse modification of Critical Habitat (50 CFR 402),
and to utilize their authorities to carry out programs for the
conservation of the species.
Status - 1 (DRAFT) - Status
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
STATE STATUSES AND LAWS:
STATE: Utah
DESIGNATED STATUS: Protected, Recognized Threatened
ADMINISTRATIVE AGENCY: Utah Department of Natural Resources,
Division of Wildlife Resources.
STATE STATUTE: Proclamation of Wildlife Board for amphibiians
and Reptiles Sept. 1, 1979, Utah Code Annotated,
23-13-2 to 23-13-4.
INTERNATIONAL STATUSES, TREATIES, AND AGREEMENTS:
CITES-II, February 4, 1977.
ECONOMIC STATUSES:
The species provided some commercial value in the past by sale as
pets. It is now considered a competitor with cattle and sheep for
rangeland by local ranchers.
77/02/22:42 FR 10462/10487 - Implementation CITES - CITES II
78/08/23:43 FR 37662/37665 - Proposed listing as Endangered w/ CH
79/03/06:44 FR 12382/12384 - Suppl. info. for Critical Habitat desig.
79/12/07:44 FR 70680/70682 - Repropose to determine Critical Habitat
80/08/20:45 FR 55654/55666 - Final Rule, Threatened with Critical Hab.
85/07/22:50 FR 29901/29909 - Five year review
Status - 2 HABITAT ASSOCIATIONS
HABITAT - TERRESTRIAL
TERRESTRIAL
LAND USE -
Transportation, communications, and Util
Shrub and Brush Rangeland
COMMENTS ON HABITAT ASSOCIATIONS -
The Beaver Dam Slope is the northeastern extreme of the Mojave
Desert as it extends into Utah. The climate of the St. George area,
just east of the Beaver Dam Slope area, is arid and experiences a
wide degree of temperature fluctuation during the year. Annual
precipitation is approximately 7.5 inches with the greatest monthly
average in March (0.9 inches) and the least in June (0.2 inches).
Annual temperature average in January is 38 F. The mean maximum and
minimum temperatures are 116 F and -11 F, respectively (01).
The Beaver Dam Slope is composed of Quaternary alluvial deposits,
with a few Precambrian and Carboniferous outcrops. In many areas,
conglomerate caliche layers up to five feet thick have formed. The
area is dissected by several washes draining to the west and southwest
and eventually into a major streambed, the Beaver Dam Wash. The slope
ranges from 2400 to 4000 feet in elevation (01).
Based on dominant plant species, five major vegetation zones may
be recognized in the area. Tortoises are most often associated with
the joshua tree (Yucca brevifolia) - creosote (Larrea divaricata) and
creosote - bromegrass (Bromus spp.) zones. However, one concentration
of tortoises occurs west of the Beaver Dam Wash in a zone of scant
vegetation characterized by Eriogonum species and a variety of
annuals (01). Annual vegetation is important which is why this
species occurs in areas with very little perennial vegetation.
The burrowing habits of tortoises represent unique adaptations to
their extreme environment. Burrows function primarily as
thermo-regulatory aids and may also aid in water conservation and
protection from predators. Burrow use is temporary, generally
receiving only a few weeks use, and burrows are usually located near
bushes. Winter dens, located in the banks of washes, are basically
hibernacula where tortoises congregate during cold weather (01). The
holes in banks of washes are not created by tortoises, but rather are
created and maintained by periodic flooding. Suitable wintering sites
may limit tortoises throughout this region and, in part, explain a
disjunct distributional pattern. Tortoises may increase the size of
these den sites.
Utah Highway 91 was used extensively by tourists prior to the
completion of a freeway shortcut through the Virgin River Canyon in
the early 1970's. Old Mormon Road also crosses through an area of
known desert tortoise occurrence providing human access and ORV
accessiability.
Habitat Associations - 1 (DRAFT) - Food Habits
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
FOOD HABITS
TROPHIC LEVEL -
HERBIVORE
LIFESTAGE FOOD FOOD PART
General Deciduous Shrubs-Leaves/Twigs
General Deciduous Shrubs-Flowers/Fruit/Seed
General Arthropods
General Reptilia
General Aves
General Mammalia
General Poaceae
General
General Forb Leaves/Stems
General Forb Flowers/Fruit/Seed
Food Habits - 1 (DRAFT) - Environment Associations
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Terrestrial Features: Burrows
Environment Associations - 1 (DRAFT) - Life History
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
LIFE HISTORY
FOOD HABITS:
Desert tortoises are herbivorous and are opportunistic feeders,
although distinct preferences for certain plants may be exhibited.
One study found that 3 species of grasses (Aristida, Tridens, and
Bromus) accounted for 61% of the diet (01). Although their diet
included a wide variety of grasses, sedges (Carex sp.), forbs and
certain shrubs, only the succulent portions such as leaves and
flowering parts are eaten. Sand, bird feathers, mammal hairs, snake
and lizard skins, and arthropods were also found in some scats but
represented only incidental food items. Coombs (1977) found the
annual grass Bromus rubens and the annual forb cutleaf filaree
(Erodium cicutarium) to be the chief foods (02). The native perennial
grass Muhlenbergia porteri was considered an important food when
available, providing both protein and moisture even in late summer and
early fall. However, Minden (1981) found little Aristida and
Muhlenbergia in the diet. He determined Bromus to be an important
food item throughout the spring. Various perennial grasses seemed of
moderate importance in early spring, but were replaced by heavy use of
forbs in May and June (03). This may reflect energy available in
perennial versus annual seeds. Annual seeds, for the most part, yield
higher energy per unit volume than perennial seeds. In a 1980 study,
Minden found that a milkvetch, Astragalus nuttalianus, an annual forb,
was the preferred spring forage, making up 59% of the diet (04).
Peak tortoise activity usually coincides with the abbreviated
period of annual bloom. During the blooming period, tortoises
apparently consume enough annual forage to sustain them through the
summer aestivation and winter dormancy periods (01). The spring bloom
is considered critically important to tortoise survival and
reproduction. Normal reproduction and recruitment to the population
probably depend upon an optimum combination of nutrients and moisture
in both spring and fall forage (01,02). Forage must be sufficient to
allow females to accumulate energy reserves for egg production. In
dry springs, tortoises may rely on fat reserves accumulated during
the previous spring (01).
HOME RANGE/TERRITORY:
Little is known of the territorial behavior or home range of the
desert tortoise. However, ranges of 11 adult female wild tortoises in
the spring of 1980 varied from 8.53 ha (21.07 acres) to 0.59 ha (1.46
acres) with a mean of 3.67 ha (9.03 acres) (04). In April, tortoises
remained near winter dens while foraging and returned to them for
overnight shelter. But as the season progressed, they ventured
further away and began utilizing summer burrows (04).
PERIODICITY:
Peak tortoise activity usually coincides with the annual bloom in
May-June. They apparently consume enough annual forage during this
period to sustain them through summer aestivation and winter dormancy
(01). Temperature determines daily activity. Tortoises appear to be
active when air temperatures are between 10 C (50 F) and 32 C (90 F),
or when soil temperatures are 18 C (64 F) to 48 C (118 F) (04). On
Life History - 1 (DRAFT) - Life History
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
hot days, foraging is frequently interrupted by short periods of rest
in the shade, with retreat to burrows as temperature rises or falls
beyond preferred levels. By late June, extreme heat reduces tortoise
activity significantly, limiting it to early morning, and most of
their time is spent in the shelter of summer burrows (04).
MIGRATION PATTERNS:
The desert tortoise is non-migratory.
COVER/SHELTER REQUIREMENTS:
Tortoises use 2 types of cover sites in Utah: winter dens and
summer burrows. Winter dens are permanent hibernacula where tortoises
congregate during cold weather. They are located in the banks of
washes under exposed outcroppings. They are generally occupied from
October-April and are excavated 5-30 feet into gravel banks (01).
Minden found den openings averaged 28 cm (11 in.) in height and 85 cm
(33.5 in.) in width (04). Den lengths may be up to 9 meters (30 ft.).
Twelve different plant species were found growing near dens, but none
appeared to occur more often than another. Over 50% of den openings
faced in directions between and including east and south (04).
Tortoises modify these sites but many are natural crevices. Summer
burrows are dome-shaped hollows often located under bushes (01). They
are used by individual tortoises overnight, during brief periods of
inactivity, and for extended periods to escape extreme heat and
drought. Burrows are ephemeral and generally receive only a few weeks
use (04). They are 1-4 feet deep and show seasonal variation, being
relatively shallow in May and deeper in June as temperatures increase
(04).
REPRODUCTIVE SITE REQUIREMENTS:
Nests are dug in sandy soil using either the hind feet, or the
front legs and then the hind feet. Nests have measured 23 cm (9 in.)
in diameter at the top, 18 cm (7 in.) at the bottom and 15 cm (6 in.)
deep (01). However, depth of the nest appears to vary with size of
the female and hardness of the soil. Nest sites usually resemble
undisturbed ground, and females often urinate in the nest before and
after filling it (01).
REPRODUCTIVE CHARACTERISTICS:
Little is known regarding reproduction under natural conditions.
Peak breeding activity occurs in March-April and nesting occurs in
May-July (01). Multiple clutches occur in captive tortoises; it is
believed the same may be true of wild individuals. Clutch size varies
from 2-14 eggs with 5-6 as the average. Larger females tend to have
larger clutches (01). Incubation is 90-120 days in the wild, and
hatching occurs August-October (01). Hatchlings appear to dig or find
an existing burrow shortly after hatching and become dormant, ignoring
food and water. In some cases eggs do not hatch in the fall but
remain over the winter, with hatchlings emerging in the spring (01).
PARENTAL CARE:
No specific information on parental care is available. However,
it appears that shortly after hatching the young dig or find an
Life History - 2 (DRAFT) - Life History
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
existing burrow and begin dormancy (01). Vaughan (06) observed two
different cases where a female tortoise aggressively defended her
eggs against Gila monsters.
POPULATION BIOLOGY:
Few exact population parameters of the desert tortoise are known
except that the species is long-lived and, according to a 1980 study
by Minden, exhibits a balanced sex ratio (04,05). The latest survey
revealed a total of 82 tortoises over a 30 square mile area (04,05).
Past studies show the Beaver Dam Slope population to be declining
steadily (01). Limiting factors include habitat destruction,
competition for food with cattle and sheep, a low recruitment rate,
few eggs produced, and slowness in reaching sexual maturity (01).
Natural predation by the kit fox, coyote, and Gila monster may be
significant depending on the age class of the tortoise involved (05,
06).
The objective under management is to restore the Beaver Dam Slope
population to non-endangered status by establishing and maintaining a
viable, self-sustaining population (01).
SPECIES INTERRELATIONSHIPS:
Woodrats (Neotoma lepida) are common commensals, building their
nests in the mouths of tortoise dens (05). Other small vertebrates
and invertebrates may also inhabit burrows. The kit fox (Vulpes
macrotis) often utilizes tortoise burrows and may be the most
important predator. Coyotes (Canis latrans) and Gila monsters may also
be significant predators of the tortoise (05).
OTHER LIFE HISTORY DESCRIPTORS:
None.
Life History - 3 (DRAFT) - Management Practices
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Controlling/Restricting Off-Road Vehicles
Beneficial Restricting/regulating human disturbance of populations
Beneficial Controlling/Restricting Road Maintainance Actions
Beneficial Controlling/Restricting Agricultural Practice
Beneficial Creating Artificial Habitat/Nesting Structure
Beneficial Reforestation
Beneficial Transplanting wild animals
Beneficial Transplanting Wild Eggs/Wild Seeds
Beneficial Restricting Poaching
Beneficial Controlling/Removing Native Vertebrates
Beneficial Controlling/Removing Domestic Animals
Adverse Collecting
Existing Collecting
Adverse Commercial Exploitation
Existing Commercial Exploitation
Adverse Inherent Reproductive Characteristics
Existing Inherent Reproductive Characteristics
Adverse Predation
Existing Predation
Adverse Competition
Existing Competition
Adverse Grazing
Existing Grazing
COMMENTS ON MANAGEMENT PRACTICES -
The Beaver Dam Slope has a long history of abusive grazing
practices (grazing). Both sheep and cattle used the area annually
from the late 1800's until the late 1960's, resulting in clear
overgrazing of tortoise habitat. A 1948 study reported that tortoises
had only a 30-40 day spring green period before sheep swept the area
clean of annuals (01,02). Cattle are now greatly reducing the
availability of perennial grasses. Dietary overlap of 37.7 percent
between tortoises and cattle has been reported (competition) (02).
Grazing by domestic animals has also resulted in trampling and actual
destruction of food plants, shelter, and denning sites.
Overcollecting of tortoises for sale as pets has been a major
detrimental factor. Prior to the early 1970's it was common practice
for service station operators to collect and sell tortoises to
tourists.
Desert tortoises are generally believed to be long-lived, slow to
reach sexual maturity, produce relatively few eggs, and have a low
recruitment rate, increasing their vulnerability to other factors.
Natural predation by the kit fox, coyote, and Gila monster may be
a significant factor in the decline of the species, depending on age
class involved (01).
UNAPPROVED PLAN:
Management Practices - 1 (DRAFT) - Management Practices
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
U.S. Fish and Wildlife Service. 1984. The Desert Tortoise Recovery
Plan (Beaver Dam Slope Population). Agency Draft. U.S. Fish and
Wildlife Service, Denver, CO. 63 pp.
Recovery actions proposed for the Beaver Dam Slope population
of the desert tortoise include:
1) Determining its status and specific population trends for all
age groups.
2) Determining specific habits and habitat requirements for all
age groups by monitoring environmental characteristics of high and low
tortoise use areas, and conducting studies on the life history of the
species. Needed studies include; hatching success, age and growth
rates, clutch size, and age to sexual maturity.
3) Determining extrinsic factors limiting the population.
Limiting factors on the population will be studied, including: impacts
on habitat and food supply by grazing; the effects of predation; and
the extent of ORV caused damage or mortality and need to control or
restrict ORV use. Annual vegetation, versus perennial, production is
imperative to the desert tortoise survival. The controlling of future
agricultural practices towards annual vegetation may be desirable.
4) The existing Beaver Dam Slope population and habitat within
the designated Critical Habitat area will be preserved and protected.
This also includies the restricting of surface-disturbing activities
(such as limiting human access by controlling/restricting road
maintenance activities and agricultural practices) when tortoises are
most active. Utah Highway 91 was used extensively by tourists prior
to the completion of a freeway shortcut through the Virgin River
Canyon in the early 1970's. At one time gas station attendents
collected and sold tortoises to tourists along this route.
Old Mormon Road also crosses through an area of known desert tortoise
occurrence providing human access and ORV accessability.
5) Current habitat will be improved, possibly by enlarging or
creating new dens, providing water for tortoise use, managing
livestock to allow improvement of desert tortoise habitat, and
improving vegetative composition and biomass. Mortality may be
controlled by controlling or reducing predator populations within the
Critical Habitat. Tortoise population numbers may be augmented by
some artificial hatching of wild eggs.
Management Practices - 2 (DRAFT) - References
Species TORTOISE, DESERT
Species Id ESIS156001
Date 14 MAR 96
References
*****REFERENCES FOR ALL NARRATIVES EXCEPT N-OCCURRENCE*****
01 U.S. Fish and Wildlife Service. 1984. Desert Tortoise Recovery
Plan (Beaver Dam Slope Population). Agency Draft. Prepared by
Region 6, U.S. Fish and Wildlife Service, Denver, CO.
02 Coombs, E.M. 1977. Wildlife observations of the hot desert
region, Washington Co., UT, with emphasis on reptilian species and
their habitat in relation to livestock grazing. UT Division of
Wildlife Resources. Unpub. report.
03 Minden, R.L. and S.M. Keller. 1981. Population analysis of the
desert tortoise (Gopherus agassizii) of the Beaver Dam Slope,
Washington Co., UT. UT State Dept. of Nat. Resources and Energy.
No. 81-14. 49 pp.
04 Minden, R.L. 1980. Investigations of the desert tortoise
(Gopherus agassizii) on the Beaver Dam Slope, Washington Co., UT.
UT State Division of Wildl. Resources No. 80-21. 44 pp.
05 U.S. Fish and Wildlife Service. 1980. Environmental assessment;
determination that the Beaver Dam Slope population of the desert
tortoise is a Threatened species pursuant to the Endangered
Species Act of 1973 with Critical Habitat. U.S. Dept. Interior,
Washington, D.C. 25 pp.
06 Vaughan, S. 1986. Observations of aggressive behavior in desert
tortoises. Southwest. Nat. In press.
07 Bramble, D.M. 1986. Systematics, biogeography and evolution of
gopher tortoise. Proceedings of the Eleventh Annual Meeting and
Symposium of the Desert Fish Council.
*****REFERENCES FOR N-OCCURRENCE NARRATIVE ONLY*****
01 U.S. Fish and Wildlife Service. 1984. Desert Tortoise Recovery
Plan (Beaver Dam Slope Population). Agency Draft. Prepared by
the U.S. Fish and Wildlife Service, Region 6, Denver, CO. 31 pp.
02 U.S. Fish and Wildlife Service. 1980. Environmental assessment;
determination that the Beaver Dam Slope population of the desert
tortoise is a Threatened species pursuant to the Endangered
Species Act of 1973 with Critical Habitat. U.S. Dept. Interior.
Washington, D.C. 25 pp.
References - 1